In processing crude oil in refinery operations, the presence of intractable emulsions of high specific gravity crude oils often present serious problems leading to oil losses, contamination problems, corrosion, fouling or plugging problems, and expensive environmental treatment/disposal costs. These emulsions can arise during early processing steps at the refinery such as desalting and can also result from the collection of slop oil emulsions from all parts of the refinery. Many produced crude oils contain soluble inorganic salts, such as sodium chloride, calcium chloride, magnesium chloride or sulfate. The presence of such salts in a crude oil is very deleterious to the processing of the oil in a refinery, causing severe corrosion, poor cracking yields, plugging and ultimately equipment failure. It is therefore customary to desalt incoming crude at a refinery by mixing the crude with wash water and allowing the water phase to dissolve the salt and be separated in a desalter vessel.
The intractable emulsions of oil, water and solids make adequate separation and oil recovery difficult. Often, the only answer is that such emulsions arising from desalter are periodically discarded as are other intractable emulsions and slop streams throughout the refinery. This results in expensive treating or handling procedures or pollution problems as well as the fact that processable crude oil is also lost with these intractable emulsions and slop streams.
In most cases, complete separation of water from the oil is inhibited by the presence of an envelope of solid or semi-solid material in a thin-film layer around the surface of each individual water droplet. This material may be inorganic, for example as clay platelets, or silica or limestone particles, or it may be organic such as wax-like or bitumen-like particles. These inorganic and organic solids act as emulsion stabilizers. Furthermore, if the oil has a specific gravity approaching that of water and has a high viscosity, the difficulty of separating these types of oil emulsions is further compounded. The high viscosity greatly hampers the effectiveness of separation equipment.
U.S. Pat. No. 4,938,876 describes a process whereby emulsions can generally be broken by causing a portion of the normally water dispersed phase to flash into vapor by suddenly reducing pressure on the emulsion (flashing) as described in the patent. The flashing action is extremely powerful even when only a small fraction, 10 percent by volume or less, of the dispersed phase is vaporized. The envelope around each droplet is thus shattered so the dispersed phase can be coalesced and separated by gravity, or enhanced gravity forces, when there is a sufficient divergence of specific gravity and a low viscosity. Suitable anti-emulsion chemicals are often added to prevent re-emulsification. The process of the above mentioned patent is successfully operated on a wide variety of intractable emulsion/suspensions, but has been found deficient when the components of the emulsion are not amenable to gravity separation as mentioned above. The patent does not tell one skilled in the art how to deal with the problem of emulsified high specific gravity oil, and only combats high viscosity by heating.
Accordingly, it is an object of this invention to provide a process whereby the components of slop oil emulsions can be readily separated from each other after the emulsion is broken. It is a further object of this invention to provide a process whereby crude oil may be recovered from intractable refinery emulsions for refining as a product. It is a further object of this invention to provide not only for the maximum recovery of oil from refinery waste emulsions, but to allow for environmentally-benign disposal of solids and aqueous components of such waste.
The foregoing objects and other objects which will become obvious to those of ordinary skill in the art after considering this description and drawings of how this advantage is accomplished by the following-described invention.